R help - Jan 2008 - Multiplying each row of a big matrix with a vector

I have a big matrix 'ret'. I want to multiply each row of it with a 2nd
vector 'pos', resulting result, I want to save in a vector named
'port'. I wrote following code:
   
  > pos
[1]  2593419  2130220  6198197  1673888  1980000  1784732  2052120 -7490228
-5275000

   
  > dim(ret)
[1] 500   9

  > fu    # user defined function
function(x)
   {
    fu = x %*% t(pos)
   }
port = apply(ret, 1, fu)

  > dim(port)
[1]  81 500

  My desire is to get port as a vector with length 500. However I am not getting
that?
   
  Can anyone tell me how to correct that? 
   
  Regards,
   

       
---------------------------------

	[[alternative HTML version deleted]]

port <- as.vector(ret %*% port)

should do it. 


Bill Venables

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Megh Dal
Sent: Wednesday, 30 January 2008 5:20 PM
To: r-help at stat.math.ethz.ch
Subject: [R] Multiplying each row of a big matrix with a vector

I have a big matrix 'ret'. I want to multiply each row of it with a 2nd
vector 'pos', resulting result, I want to save in a vector named
'port'.
I wrote following code:
   
  > pos
[1]  2593419  2130220  6198197  1673888  1980000  1784732  2052120
-7490228 -5275000

   
  > dim(ret)
[1] 500   9

  > fu    # user defined function
function(x)
   {
    fu = x %*% t(pos)
   }
port = apply(ret, 1, fu)

  > dim(port)
[1]  81 500

  My desire is to get port as a vector with length 500. However I am not
getting that?
   
  Can anyone tell me how to correct that? 
   
  Regards,
   

       
---------------------------------

	[[alternative HTML version deleted]]

______________________________________________
R-help at r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

I am not sure if you really want what you explain that you want

To multiply each row with a vector you can use e.g.

t(apply(ret,1, function(y) pos*y))

or

t(t(ret)*pos)

but then you will get the same matrix just multiplied by a vector.

If you want to perform matrix multiplication then just

ret %*% pos will do it for you

Petr Pikal
petr.pikal at precheza.cz

r-help-bounces at r-project.org napsal dne 30.01.2008 08:20:21:
> I have a big matrix 'ret'. I want to multiply each row of it with a
2nd
vector
> 'pos', resulting result, I want to save in a vector named
'port'. I
wrote 
> following code:
> 
>   > pos
> [1]  2593419  2130220  6198197  1673888  1980000  1784732  2052120 
-7490228 -5275000
> 
> 
>   > dim(ret)
> [1] 500   9
> 
>   > fu    # user defined function
> function(x)
>    {
>     fu = x %*% t(pos)
>    }
> port = apply(ret, 1, fu)
> 
>   > dim(port)
> [1]  81 500
> 
>   My desire is to get port as a vector with length 500. However I am not 
getting that?
> 
>   Can anyone tell me how to correct that? 
> 
>   Regards,
> 
> 
> 
> ---------------------------------
> 
>    [[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide 
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

hits=-2.6 tests=BAYES_00
X-USF-Spam-Flag: NO

[this after a mistakenly private email to Megh]

As others have said,   "%*%" is sufficiently vectorized to do
what you want.

Speaking as a reformed Matlab user,
it might be as well to add that the  definition of function fu()
that you give looks like matlab code to me.


Check this out:


 > f <- function(x){f = x^2}
 > f(4)
 >
 > dput(f(4))
16
 >


Thus fu() returns 16 but invisibly.  This can be terribly
confusing to those from a matlab background.



In R, one can just write

 > f<- function(x){x^2}

because functions return the last evaluated expression.

Compare matlab, where(IIRC) one has to state in the function
the name of the variable whose value will be returned.


HTH

rksh





On 30 Jan 2008, at 07:20, Megh Dal wrote:
> I have a big matrix 'ret'. I want to multiply each row of it with a
> 2nd vector 'pos', resulting result, I want to save in a vector
named
> 'port'. I wrote following code:
>
>> pos
> [1]  2593419  2130220  6198197  1673888  1980000  1784732  2052120  
> -7490228 -5275000
>
>
>> dim(ret)
> [1] 500   9
>
>> fu    # user defined function
> function(x)
>   {
>    fu = x %*% t(pos)
>   }
> port = apply(ret, 1, fu)
>
>> dim(port)
> [1]  81 500
>
>  My desire is to get port as a vector with length 500. However I am  
> not getting that?
>
>  Can anyone tell me how to correct that?
>
>  Regards,
>
>
>
> ---------------------------------
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
--
Robin Hankin
Uncertainty Analyst and Neutral Theorist,
National Oceanography Centre, Southampton
European Way, Southampton SO14 3ZH, UK
  tel  023-8059-7743

Ret= matrix(sample( 1:1000, 500*9), nrow=500, ncol=9)


Pos= c(  2593419  ,2130220,  6198197,  1673888,  1980000 , 1784732 ,
2052120 ,-7490228 ,-5275000)


Solution = Ret * matrix( rep(Pos, 500), nrow=500, byrow=TRUE)
Use the element-wise multiplication rather than a matrix multiplication.
Hope this helps.
Mama 

-----
Mama Attiglah, PhD
Advanced Research Center
Quantitative Research Analyst
State Street Bank
+44(0)20 7698 6290 (Direct Line)
+44 (0)207 004 2968 (Direct Fax)
Please visit our Web site at 
www.ssga.com

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Megh Dal
Sent: 30 January 2008 07:20
To: r-help at stat.math.ethz.ch
Subject: [R] Multiplying each row of a big matrix with a vector

I have a big matrix 'ret'. I want to multiply each row of it with a 2nd
vector 'pos', resulting result, I want to save in a vector named
'port'.
I wrote following code:
   
  > pos
[1]  2593419  2130220  6198197  1673888  1980000  1784732  2052120
-7490228 -5275000

   
  > dim(ret)
[1] 500   9

  > fu    # user defined function
function(x)
   {
    fu = x %*% t(pos)
   }
port = apply(ret, 1, fu)

  > dim(port)
[1]  81 500

  My desire is to get port as a vector with length 500. However I am not
getting that?
   
  Can anyone tell me how to correct that? 
   
  Regards,
   

       
---------------------------------

	[[alternative HTML version deleted]]

______________________________________________
R-help at r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.